Hybrid Spinel Oxides/N‐Doped Reduced Graphene Oxide as Highly‐Active Bifunctional Electrocatalysts for Oxygen Reduction/Evolution Reactions

Abstract

A series of Co3O4–MnCo2O4/N‐doped reduced graphene oxide (CMO/N‐rGO) electrocatalysts with different N‐rGO content were developed by using a two‐step synthetic method. The electrocatalysts were characterized by X‐ray diffraction, scanning electron microscopy/transmission electron microscopy, and X‐ray photoelectron spectroscopy. Their catalytic activities toward the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) were evaluated by linear‐sweep voltammetry (LSV) in an alkaline electrolyte. It is found that GO is vital for the formation of CMO/N‐rGO nanocomposite during the preparation. The CMO hybrid nanoparticles can be obtained through feeding GO during the preparation, but only the single spinel oxide, i.e. MnCo2O4, is formed without adding GO, even if the feeding molar ratio of Co and Mn (Co/Mn) is higher than 2. The CMO/N‐rGO nanocomposite electrocatalysts can efficiently take advantages of ORR and OER active sites from the CMO hybrid oxides and N‐rGO, as well as the enhanced charge transfer from N‐rGO, thus bringing about higher bifunctional activities towards ORR/OER in alkaline electrolyte, as compared with Co3O4, MnCo2O4, and N‐rGO. The CMO/N‐rGO nanocomposites are considered to be promising bifunctional electrocatalysts for ORR/OER.

Electrocatalytic Activity of Ionic‐Liquid‐Derived Porous Carbon Materials for the Oxygen Reduction Reaction

“…It is also worth mentioning that ORR onset potential at Carb‐IL is comparable or positive compared to onset potential values observed at carbon materials with noble metals such as palladium‐graphitic carbon nitride nanocomposite (0.9 V), Ag‐MWCNT (0.8 V), Au‐graphene (0.71 V) and metals such as cobalt‐nitrogen doped carbon (0.86 V) and cobalt‐nitrogen doped reduced graphene oxide (0.9 V) ,. ORR activity of easily prepared Carb‐IL is better or similar compared to series of nanocomposite Co 3 O 4 ‐MnCo 2 O 4 /N‐doped reduced graphene oxide electrocatalysts . Carbon materials prepared by carbonization of other ILs showed similar properties in terms of the ORR onset potential and mechanism.…”

“…Number of electrons obtained for HTC suggests co‐existence of two‐ and four‐electron ORR pathway at this material . Electrocatalysts efficiency for the ORR, i. e., the amount of HO 2 − generated is, to a great extent, governed by structure and thickness of the active layer.…”

“…Also, higher single Tafel slope was reported for mesoporous carbon framework and mesoporous graphene framework (124 mV dec −1 ) and for nitrogen‐doped mesoporous graphene framework (115 mV dec −1 ) . Other nitrogen co‐doped carbon materials showed lower Tafel slopes between 60–120 mV dec −1 such as: nitrogen‐doped reduced graphene oxide (71.2 mV dec −1 ), nitrogen‐doped carbon nanotubes (65 and 113.8 mV dec −1 ), ferrocene‐based and iron(II) phthalocyanine‐based nitrogen doped carbon nanotube (65 and 136 mV dec −1 and 87 and 171 mV dec −1 , respectively) ,,. Variation in coverage of adsorbed oxygen species could be described by Tafel slope and high values of obtained Tafel slopes in the range from 85.2 mV dec −1 to 198.0 mV dec −1 could indicate inefficient coverage of the adsorbed intermediates .…”

Crystal‐Plane‐Dependent Activity of Spinel Co3O4 Towards Water Splitting and the Oxygen Reduction Reaction

“…The Co 3 O 4 nanocrystals are also potential alternates for novel metal Pt to catalyze ORR, but the activity and stability are still inferior to commercial Pt/C in fuel cell operation . To enhance the ORR electrocatalytic performance of Co 3 O 4 , various approaches have been adopted, such as crystal‐plane‐ or morphology‐controlled, size‐controlled, electroconductivity‐enhanced and doping . Nevertheless, to the best of our knowledge, the effect of electrocatalytic activity for ORR only caused by the shift on crystal planes of Co 3 O 4 has not yet been reported.…”

Electrochemically activated surface reconstruction of OER catalyst by Cr leaching

“…48 Moreover, metallic doping of cobalt and iron based spinel with for example Ni, Mn, Cu etc, were studied for catalytic performance as well. 10,49,50 It was reported that for MFe2O4 (where M= Mn, Cu, Ni, Co) follows a trend of Co>Cu>Ni>Mn for OER activity. 16 Similarly, for cobalt based spinels, OER performance has increased with doping Ni, Cu, Li except Mn, 51 Overall, bimetallic spinel oxides proven to have better OER performance than single metal spinel M3O4 due to the synergy created using different metals ions as they might have an impact in optimising adsorption energy.…”